Personally i'm an ATI man. If you play FFXI on the PC then i would suggest going with Nvida, cause getting a driver to make FFXI run correctly has proven to be a bitch, and when you do find an ok Driver for it, it still dosn't compare to how a 400 Nvida can do it.
Nvidia's SLI (*drool*) sounds great if you're a CG artist. Only for for fact it will rip render time in half. A faster graphics card dosn't mean it will make the game/task look better. And if a single card can handle the game it's running, then the SLI is complete overkill and would show no face.